1. Field of the Invention
The present invention is directed to a wireless sensor device, and more particularly to such a wireless device including a power generating element that converts an external energy into an electric power for transmitting a sensed result as a radio signal.
2. Description of the Related Art
Japanese Patent Publication No. 2004-24551 discloses a self-contained sensing system including a power generating means for transmitting a sensed result. The system includes a sensor for sensing a temperature, an acceleration, or infrared ray to provide a sensor signal indicative of a sensed analog value, and an A/D converter which converts the sensor signal into digital data. The digital data are processed by a microprocessor so as to be transmitted through a radio transmitter as a radio signal. A solar cell is included as the power generating means in order to supply an operating power to the A/D converter, the microprocessor, and the radio transmitter. Because of that the solar cell is not expected to constantly generate sufficient power to keep the system operative, the system requires a power regulator which enables operation only while much power is being generated at the solar cell in order to transmit a reliable sensor result. Also because of that the radio transmitter along with the A/D converter consumes relatively large electric power, the system suggests the use of a wireless transmission technology generally known as UWB (Ultra Wide Band) transmission which operates at a low power. However, there is still a need of minimizing the operating power in the wireless sensor system, particularly in case that the A/D converter is not necessary and only one-bit information is sufficient as the sensor result, in order to keep a reliable sensing operation over an extended period of time while relying upon the power generator of limited power generating capacity.